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Skeletal Muscle Energy Cycle

Skeletal Muscle Energy Cycle - 3 The energy stored in the...

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Skeletal Muscle Energy Cycle ‘Cheat Sheet’ Given: 1. High concentration of ATP in muscle fiber. 2. Very low free Ca++ - actin binding sites blocked so no actin/myosin bonding possible State: The binding sites for ATP on the myosin head group are filled and the reaction ATP > ADP + Pi has taken place although the reaction products are still bound to the myosin. The myosin is energetically charged. Given: 1. Stimulation has caused Ca++ to be released from the sarcoplasmic reticulum raising the level of free intracellular calcium. Time Sequence. 1. The calcium binds to the troponin complex of on the actin filament which leads to ‘unshielding’ of the actin binding site. 2. The myosin binds to the actin.
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Unformatted text preview: 3. The energy stored in the myosin is released as the myosin pulls on the actin fiber. 4. At the same time the ADP is released from the myosin exposing an ATP binding site. 5. ATP binds to the myosin. 6. The actin/myosin bond is broken with myosin returning to its ‘relaxed’ state. 7. The attached ATP is hydrolyzed recharging the myosin. 8. If it can, the myosin binds to the actin returning to number 3 above. The cycle continues as long as actin and myosin can bind which depends on Ca++ being bound to troponin (i.e. the level of free calcium remains high). Note that in the absence of ATP, the actin/myosin bond cannot be broken. This is the cause of Rigor Mortis....
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